Fixed pa_win_wmme.c latency calculations to result in non-decreasing actual latency for increasing suggested latency.
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rossb
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d15c703f8f
commit
903263d777
1 changed files with 46 additions and 42 deletions
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@ -1341,13 +1341,9 @@ static unsigned long ComputeHostBufferCountForFixedBufferSizeFrames(
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/* Calculate the number of buffers of length hostFramesPerBuffer
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that fit in suggestedLatencyFrames, rounding up to the next integer.
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The exact formula for round-up is:
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((suggestedLatencyFrames + (hostFramesPerBuffer - 1)) / hostFramesPerBuffer)
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However we subtract 2 instead of 1 below to account for rounding errors.
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This ensures we don't erroneously overallocate an extra buffer due to a one-sample rounding error.
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The value (hostBufferSizeFrames - 1) below is to ensure the buffer count is rounded up.
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*/
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unsigned long resultBufferCount = ((suggestedLatencyFrames + (hostBufferSizeFrames - 2)) / hostBufferSizeFrames);
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unsigned long resultBufferCount = ((suggestedLatencyFrames + (hostBufferSizeFrames - 1)) / hostBufferSizeFrames);
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/* We always need one extra buffer for processing while the rest are queued/playing.
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i.e. latency is framesPerBuffer * (bufferCount - 1)
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@ -1370,61 +1366,69 @@ static PaError SelectHostBufferSizeFramesAndHostBufferCount(
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unsigned long *hostBufferSizeFrames,
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unsigned long *hostBufferCount )
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{
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unsigned long effectiveUserFramesPerBuffer;
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unsigned long numberOfUserBuffersPerHostBuffer;
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if( userFramesPerBuffer == paFramesPerBufferUnspecified ){
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*hostBufferSizeFrames = PA_MME_HOST_BUFFER_GRANULARITY_FRAMES_WHEN_UNSPECIFIED_;
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effectiveUserFramesPerBuffer = PA_MME_HOST_BUFFER_GRANULARITY_FRAMES_WHEN_UNSPECIFIED_;
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}else{
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*hostBufferSizeFrames = userFramesPerBuffer;
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effectiveUserFramesPerBuffer = userFramesPerBuffer;
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if( *hostBufferSizeFrames > absoluteMaximumBufferSizeFrames ){
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/* user has requested a user buffer that's larger than what we can handle */
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if( effectiveUserFramesPerBuffer > absoluteMaximumBufferSizeFrames ){
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/* user has requested a user buffer that's larger than absoluteMaximumBufferSizeFrames */
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/* @todo FIXME right now we allow the user to request an oversize host buffer,
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/* @todo FIXME/REVIEW right now we allow the user to request an oversize host buffer,
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even though elsewhere in the code there are suggestions that oversize buffers
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can cause crashes with some drivers. */
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can cause crashes with some drivers. see http://www.portaudio.com/trac/ticket/189
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*/
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/* return paBufferTooBig; */
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}
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}
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/* compute a host buffer count based on suggestedLatencyFrames and our granularity */
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*hostBufferSizeFrames = effectiveUserFramesPerBuffer;
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*hostBufferCount = ComputeHostBufferCountForFixedBufferSizeFrames(
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suggestedLatencyFrames, *hostBufferSizeFrames, minimumBufferCount );
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/* consider coalescing multiple user buffers into each host buffer */
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/*
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If there are too many host buffers we would like to coalesce
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them by packing an integer number of user buffers into each host buffer.
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We try to coalesce such that hostBufferCount will lie between
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PA_MME_TARGET_HOST_BUFFER_COUNT_ and (PA_MME_TARGET_HOST_BUFFER_COUNT_*2)-1.
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We limit coalescing to avoid exceeding either absoluteMaximumBufferSizeFrames and
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preferredMaximumBufferSizeFrames.
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if( *hostBufferCount >= PA_MME_TARGET_HOST_BUFFER_COUNT_ * 2 ){
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/* If there are too many host buffers we would like to coalesce
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them by packing an integer number of user buffers into each host buffer.
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We try to coalesce such that hostBufferCount will lie between
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PA_MME_TARGET_HOST_BUFFER_COUNT_ and (PA_MME_TARGET_HOST_BUFFER_COUNT_*2)-1.
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We limit coalescing to avoid exceeding either absoluteMaximumBufferSizeFrames and
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preferredMaximumBufferSizeFrames.
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*/
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First, compute a coalescing factor: the number of user buffers per host buffer.
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The goal is to achieve PA_MME_TARGET_HOST_BUFFER_COUNT_ total buffer count.
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Since our latency is computed based on (*hostBufferCount - 1) we compute a
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coalescing factor based on (*hostBufferCount - 1) and (PA_MME_TARGET_HOST_BUFFER_COUNT_-1).
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unsigned long maxCoalescedBufferSizeFrames = (absoluteMaximumBufferSizeFrames < preferredMaximumBufferSizeFrames) /* min of our limits */
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? absoluteMaximumBufferSizeFrames
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: preferredMaximumBufferSizeFrames;
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The + (PA_MME_TARGET_HOST_BUFFER_COUNT_-2) term below is intended to round up.
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*/
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numberOfUserBuffersPerHostBuffer = ((*hostBufferCount - 1) + (PA_MME_TARGET_HOST_BUFFER_COUNT_-2)) / (PA_MME_TARGET_HOST_BUFFER_COUNT_ - 1);
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if( numberOfUserBuffersPerHostBuffer > 1 )
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{
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unsigned long maxCoalescedBufferSizeFrames = (absoluteMaximumBufferSizeFrames < preferredMaximumBufferSizeFrames) /* minimum of our limits */
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? absoluteMaximumBufferSizeFrames
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: preferredMaximumBufferSizeFrames;
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unsigned long maxUserBuffersPerHostBuffer = maxCoalescedBufferSizeFrames / *hostBufferSizeFrames; /* don't coalesce more than this */
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unsigned long maxUserBuffersPerHostBuffer = maxCoalescedBufferSizeFrames / effectiveUserFramesPerBuffer; /* don't coalesce more than this */
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/* we truncate here to compute a conservative value of numUserBuffersPerHostBuffer
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then we recompute hostBufferCount after coalescing.
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*/
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unsigned long numUserBuffersPerHostBuffer = *hostBufferCount / PA_MME_TARGET_HOST_BUFFER_COUNT_;
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if( numUserBuffersPerHostBuffer > maxUserBuffersPerHostBuffer )
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numUserBuffersPerHostBuffer = maxUserBuffersPerHostBuffer;
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if( numberOfUserBuffersPerHostBuffer > maxUserBuffersPerHostBuffer )
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numberOfUserBuffersPerHostBuffer = maxUserBuffersPerHostBuffer;
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if( numUserBuffersPerHostBuffer > 1 ){
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*hostBufferSizeFrames *= numUserBuffersPerHostBuffer;
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*hostBufferSizeFrames = effectiveUserFramesPerBuffer * numberOfUserBuffersPerHostBuffer;
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/* recompute hostBufferCount to approximate suggestedLatencyFrames now that hostBufferSizeFrames is larger */
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*hostBufferCount = ComputeHostBufferCountForFixedBufferSizeFrames(
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suggestedLatencyFrames, *hostBufferSizeFrames, minimumBufferCount );
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}
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/* recompute hostBufferCount to approximate suggestedLatencyFrames now that hostBufferSizeFrames is larger */
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*hostBufferCount = ComputeHostBufferCountForFixedBufferSizeFrames(
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suggestedLatencyFrames, *hostBufferSizeFrames, minimumBufferCount );
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}
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return paNoError;
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@ -1515,7 +1519,7 @@ static PaError CalculateBufferSettings(
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: PA_MME_MIN_HOST_INPUT_BUFFER_COUNT_HALF_DUPLEX_;
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result = SelectHostBufferSizeFramesAndHostBufferCount(
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(unsigned long)(suggestedInputLatency * sampleRate),
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(unsigned long)(suggestedInputLatency * sampleRate), /* (truncate) */
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userFramesPerBuffer,
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minimumBufferCount,
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(unsigned long)(PA_MME_MAX_HOST_BUFFER_SECS_ * sampleRate), /* in frames. preferred maximum */
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@ -1610,7 +1614,7 @@ static PaError CalculateBufferSettings(
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/* compute the output buffer size and count */
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result = SelectHostBufferSizeFramesAndHostBufferCount(
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(unsigned long)(suggestedOutputLatency * sampleRate),
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(unsigned long)(suggestedOutputLatency * sampleRate), /* (truncate) */
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userFramesPerBuffer,
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PA_MME_MIN_HOST_OUTPUT_BUFFER_COUNT_,
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(unsigned long)(PA_MME_MAX_HOST_BUFFER_SECS_ * sampleRate), /* in frames. preferred maximum */
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